How do you enter the command for a cube root?

Question

Ricky Smith 2016-9-7

2
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/302317-how-do-you-enter-the-command-for-a-cube-root

回答： Hamad Al-Mulla 2021-11-24

采纳的回答： John D'Errico

I'm re-working the volume of a sphere equation (V=(4*pi*r^3)/3) to solve for the radius(r).

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

John D'Errico 2016-9-7

11
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/302317-how-do-you-enter-the-command-for-a-cube-root#answer_234138

编辑：John D'Errico 2016-9-7

在 MATLAB Online 中打开

Two simple options:

x^(1/3)

Or,

nthroot(x,3)

Be very careful though. If x is negative, it will return a complex number, because there are indeed THREE cube roots of a negative number. Two of them are complex. nthroot will give you the root you would expect however.

(-2)^(1/3)
ans =
      0.62996 +     1.0911i
nthroot(-2,3)
ans =
      -1.2599

In your case, it is not relevant, since the number will be non-negative.

2 个评论
显示无隐藏无

James Tursa 2018-11-7

编辑：James Tursa 2018-11-7

"... there are indeed THREE cube roots of a negative number ..."

To complete John's thought, there are three distinct cube roots of every non-zero number (positive real, negative real, complex), not just of the negative real numbers. And as John points out, some of these roots are complex, so you need to know how the tools you are using behave in order to get the answer(s) you want. (In general, there are n distinct n'th roots of every non-zero real or complex number)